Howto convert AVI to xvid with mencoder

As I was looking into reducing the size of a video, I felt upon this wiki page, which proved super-useful:

HOWTO Convert video files

Note: As commented by one reader, xvid is not really divx though, but changing the title and the url of my post 6 months later would just add to the confusion. Sorry about that, I wasn't meaning to confuse anyone, and I thought in good fait it was the same (the results are the same for me though: very high volume loss for very little quality loss).